1. Field of the Invention
The present invention relates to an apparatus and a method for manufacturing semiconductor devices
2. Description of the Related Art
As performance of large scale integrated circuits (LSI) improves, a density of component integration or a finer design of components included in LSI has been increased. In order to realize finer components, it is necessary not only to reduce an area of an impurity diffusion region in a plane pattern but also to reduce a depth of the impurity diffusion region. Therefore, it has been increasingly important to optimize ion implantation and following thermal treatment (annealing) when creating an impurity diffusion region such as a source/drain region and a functional region such as a channel region that is immediately below a gate insulator.
Annealing has been conducted under conditions of, for example, 1000 degrees centigrade for 30 minutes. However, annealing in such high-temperature and long-period conditions causes both activation and diffusion of an impurity at the same time. Hence, a rapid thermal annealing (RTA) method using a tungsten (W) halogen lamp or the like under conditions of 1000 degrees centigrade for about 10 seconds has been introduced as a treatment method in a minimum duration to achieve activation of an impurity while minimizing impurity diffusion. However, even with RTA, impurity diffusion still happens after annealing, and therefore it is difficult to obtain a desired impurity profile.
Laser annealing has been considered as a method for instantaneously supplying energy which is necessary for activation. However, since laser is highly directive light, a multi-photon process or interference occurs. Moreover, an energy density of a laser beam per unit time and unit area becomes too high. As a result, a surface of a semiconductor substrate (wafer) melts, and a situation which is almost like evaporation or laser ablation is induced, thus deteriorating surface morphology of a semiconductor substrate after activation.
Apart from RTA and laser annealing, flash lamp annealing (FLA) in which the lamp is filled with gas such as xenon is attracting a great deal of attention as means for improving an activation ratio in an extremely short period. For example, conditions for flash lamp annealing are, an annealing time of 10 milliseconds or smaller, and radiant energy density of 100 J/cm2 or smaller. With FLA, diffusion of an impurity is suppressed, and at the same time, an impurity is activated. Moreover, there are no secondary deterioration effects which occur during laser annealing. Therefore, FLA has been attracting attention as a new annealing technique which forms an extremely shallow junction.
However, in a full-field exposure type annealing, typified by FLA, performed by millisecond, it is difficult to anneal the entire surface of a wafer with even temperature. For example, for FLA, one or more stick-shaped lamps are arranged to face a substrate. Light beams emitted from each lamp reach the substrate directly or indirectly via a reflection plate, and are absorbed. Light beams from the lamps radiate in every direction about the lamps. Therefore, in order to obtain an uniform light intensity over a substrate surface, it is necessary to optimize a distance between lamps and a substrate, a reflection power of a reflection plate provided on the opposite side of a substrate relative to the lamps, a distance between lamps and the reflection plate, and the like, and then arrange the lamps, substrate, and reflection plate accordingly.
However, since lamps have unavoidable variation in quality due to manufacturing processes thereof, they also vary in the conversion efficiency, in which electric power is converted into light power. Hence, even if arrangement of lamps and a substrate is designed in an ideal manner, in reality, uniformity of light intensities on a substrate is deteriorated, or, when a lamp is replaced as it reaches the end of its life, lamps lose uniformity. Pre-heating a substrate to some hundreds degrees centigrade before being exposed to light by placing the substrate on a hot plate or the like is one of effective methods for improving stability during a super-short optical thermal treatment process. However, if the hot plate fails to have high uniformity of temperature, temperature that the substrate reaches as a result of light irradiation loses uniformity. In a manufacturing process for a fine semiconductor device, if temperature of thermal treatment for forming a source/drain diffusion layer is not uniform, resultant properties of manufactured transistors do not become uniform. In a semiconductor device manufacturing process where productivity is guaranteed by mass-manufacturing of a large number of chips out of a single wafer, variation in properties on the same substrate means the number of non-defective products gained from a single wafer is reduced, and as a result, this will be a factor of an increase in manufacturing costs for semiconductor devices.
In optical thermal treatment equipment which takes a few seconds or more for thermal treatment, in order to compensate variation in intensity of light from lamps, a wafer, or a substrate may be rotated while being heated. Even if there is two-dimensional irregularity of light intensity in a direction of rotating a substrate (wafer), the irregularity can be applied to each section of the semiconductor evenly by rotating the substrate. Therefore, deterioration of uniformity can be suppressed in the rotation direction of the substrate (wafer). Also employed is means for monitoring a plurality of points of a substrate and, from the monitored temperature of each point, controlling light intensities of corresponding lamps using closed-loop feedback.
However, in a case of FLA where light is emitted at millisecond, it is in fact difficult to rotate a substrate once within an extremely short period like a millisecond, and this method of substrate rotation cannot be used. Moreover, since duration of light emission is extremely short, irradiation time is not sufficient for feedback control of lamp intensity even if temperature is monitored. Therefore, it is impossible to monitor temperature with high accuracy. Moreover, even if rotation or feedback control is feasible, variation in temperature of a hot plate cannot be cancelled.